A Design Method of High-availability and Low-optical-loss Optical Aggregation Network Architecture

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1 A Desgn Method of Hgh-avalablty and Low-optcal-loss Optcal Aggregaton Network Archtecture Takehro Sato, Kuntaka Ashzawa, Kazumasa Tokuhash, Dasuke Ish, Satoru Okamoto and Naoak Yamanaka Dept. of Informaton and Computer Scence, Keo Unversty Hyosh, Kohoku, Yokohama, Kanagawa, Japan Emal: Ej Ok Dept. of Informaton and Communcaton Engneerng, The Unversty of Electro-Communcatons Chofugaoka, Chofu, Tokyo, Japan Abstract A hghly-energy-effcent network usng an optcal aggregaton network and a servce cloud has been proposed to reduce the power consumpton of today s Internet greatly. The optcal aggregaton network connects a soltary gant router to users by logcal tree topology. Ths paper proposes a novel optcal aggregaton network archtecture. The proposed archtecture uses 2x2 optcal swtches and combnes the features of a tree topology and a rng topology. The paper also ntroduces a desgn method of the proposed network archtecture. It s shown that the method can desgn hgh-avalablty and low-optcal-loss network wth fewer optcal swtches compared to a duplex tree topology. I. INTRODUCTION Recently, the number of broadband Internet subscrbers s ncreasng rapdly, and s about 300 mllon all over the world n 2007 [1]. As the broadband Internet has spread, varous servces ncludng contents delvery and vdeo conference, are provded. Today s Internet has two bg problems. The frst problem s the ncrease of power consumpton of network equpments. Worldwde power consumpton of network equpments grows about 12% per year [2]. It was 25 GW n 2008, and s expected to be over 97 GW n The second problem s the centralzng of the Internet traffc. Wth the rse of Hyper Gants ncludng Google and Akama, or the growth of cloud computng, Clent-to-Data-center traffc ncreases drastcally whle Peer-to-Peer traffc shrnks [3]. However, the current Internet topology s almost mesh, as shown n Fgure 1. Therefore, the number of hops between a user and a servce server becomes large, so RTT (Round Trp Tme) and delay jtter may affect the qualty of servces. To mprove these problems, a hghly-energy-effcent network usng an optcal aggregaton network and a servce cloud has been proposed [4]. Fgure 2 shows ts archtecture. s and servers that the current Internet contans are collected up to a soltary power-scalable gant router. Together wth servce servers, ths gant router consttutes the servce cloud. All IP traffc s aggregated by the optcal aggregaton network and transferred to the gant router n one hop. The optcal aggregaton network conssts of optcal swtches and connects the gant router to users transparently. The access method ISP : Internet Servce Provder IX : Internet exchange ISP Fg. 1. Soltary Power-scalable Gant One Hop Optcal Swtches Fg. 2. IX : Servce Servers Schematc vew of current Internet. Servce Cloud Servce Servers Optcal Aggregaton Network Hghly-energy-effcent network archtecture. s TDM (Tme Dvson Multplexng) lke a PON (Passve Optcal Network) system. Accordng to the estmate, the power consumpton of the hghly-energy-effcent network s 1/1000 of that of the present Internet [4]. Ths paper proposes a novel archtecture of the optcal aggregaton network that acheves hgh avalablty and low

2 optcal loss. A desgn method of the proposed network archtecture s also llustrated. An argument about avalablty s a great ssue n the optcal aggregaton network, because thousands of users ncludng busness users and wreless base statons are contaned n ths network by logcal tree topology. Low optcal loss between the gant router and users s also mportant, because users are wdespread, and no optcal amplfers should be utlzed preferably n terms of deployment cost. In ths paper, we consder usng Mach-Zehnder type 2x2 optcal swtches for the desgn of the optcal aggregaton network archtecture. A PLZT (Plomb Lanthanum Zrconate Ttanate) optcal swtch [5] s a typcal example of such swtch. Fgure 3 shows the archtecture of 2x2 PLZT optcal swtch. It swtches optcal sgnals n less than 10 ns when a voltage s appled to one of the electrodes. The rest of the paper s organzed as follows. Pror to the proposal, we dscuss the features of some typcal topologes n secton II. The hgh-avalablty and low-optcal-loss network archtecture for the optcal aggregaton network s presented n secton III, and ts desgn method s shown n secton IV. Fnally, we conclude the paper n secton V. Electrode P to connect N users wth the gant router. In the followng secton, t s expressed as S. The values of U and L are dfferent among users respectvely, so we evaluate these parameters by worst-case condtons, max U and max L. We focus on the feature of topology tself, and gnore any effect of other components or devces (e.g. an optcal fber cable that connects two 2x2 optcal swtches). A. Analyss 1) Tree topology: A tree topology s often used n access networks (e.g. PON). Fgure 4 shows the tree topology that s constructed by 2x2 optcal swtches. When t s a complete bnary tree, each parameter s expressed as follows. max U = 1 (1 u) log 2 N (1) max L = log 2 N l (2) S = N 1 (3) u s the unavalablty of a 2x2 optcal swtch tself, and l s the nserton loss of the optcal swtch. When N s power of two, U and L of all users are equal to max U and max L respectvely. Wavegude On Off Electrode Q (a) Archtecture Off On LT LT : Lne Termnal 2x2 Optcal Swtch (b) Cross Mode (c) Bar Mode Fg. 3. Archtecture of 2x2 PLZT optcal swtch. LT II. FEATURES OF TYPICAL TOPOLOGIES In ths secton, we evaluate the features of some typcal topologes that are constructed by 2x2 optcal swtches. We focus on the followng parameters. Unavalablty It s the probablty that a user cannot communcate wth the gant router due to a falure of a 2x2 optcal swtch. It s equal to 1 mnus avalablty. In the followng secton, the unavalablty of user ( = 0, 1, 2,..., N 1) s expressed as U. Optcal loss It s a sum of nserton losses of 2x2 optcal swtches that are placed between the gant router and a user. In the followng secton, the optcal loss between the gant router and user ( = 0, 1, 2,..., N 1) s expressed as L. Number of optcal swtches It s the number of 2x2 optcal swtches that s requred Fg. 4. Tree topology (N = 16). In the smple tree topology, at least one user becomes unable to communcate wth the gant router nevtably when any one of 2x2 optcal swtches fals. A duplex confguraton s referred as the protecton archtecture Type C to enhance the relablty of PON n ITU-T recommendaton G.983 [6]. Fgure 5 shows the duplex tree topology that s constructed by 2x2 optcal swtches. When t s a complete bnary tree, each parameter s expressed as follows. max U = (1 (1 u) log 2 N ) 2 (4) max L = log 2 N l (5) S = 2(N 1) (6)

3 Fg. 5. Duplex tree topology (N = 16). 2) Rng topology: A rng topology s often used n a metropoltan area network (e.g. ROADM (Reconfgurable Optcal Add/Drop Multplexer) rng, SONET (Synchronous Optcal Network) rng). Fgure 6 shows the rng topology that s constructed by 2x2 optcal swtches. Each parameter s expressed as follows. max U = u+(1 u)(1 (1 u) N 1 2 )(1 (1 u) N 1 2 ) (7) max L = Nl (8) S = N (9) The user that meets U = max U s = N 2 1, N 2 (when N s even) or N 1 2 (when N s odd). Equaton (7) means that the user cannot communcate wth the gant router when the 2x2 optcal swtch that s connected drectly wth the user fals, or when both of ts routes to the gant router (clockwse or counterclockwse) are unavalable concurrently due to falures of swtches on each route. The user that meets L = max L s = 0, N 1. B. Comparson Fgure 7, 8 and 9 show max U, max L and S of each topology respectvely. We assume the unavalablty of a 2x2 optcal swtch u s 10 6 and the nserton loss of the optcal swtch l s 1(dB). max U of the rng topology s lower than that of the tree topology, except when N s extremely large. Ths s because users can communcate wth the gant router by usng one of the two routes (clockwse or counterclockwse) n the rng topology. By contrast, max L of the tree topology s lower than that of the rng topology. Ths s because the number of optcal swtches that are placed between the gant router and the worst-case user s N n the rng topology, and log 2 N n the tree topology Fg. 6. Rng topology (N = 16). The duplex tree topology acheves very low max U due to settng two dfferent routes for every user that do not share any optcal swtch between the gant router and the user. However, S of ths topology s twce as many as that of the tree topology and the rng topology. Based on above argument, we propose a novel optcal aggregaton network archtecture that acheves hgh avalablty and low optcal loss together n the next secton. III. PROPOSED ARCHITECTURE Fgure 10 shows the proposed archtecture for the optcal aggregaton network. In ths archtecture, small-szed rngs are

4 Fg. 7. max U of typcal topologes. Fg. 9. S of typcal topologes. A. Constrant and objectve functon The followng constrants are set n ths method. Fg. 8. max L of typcal topologes. connected lke a tree topology by usng 2x2 optcal swtches. Fgure 10 s the proposed archtecture whose number of rng stages M s 2. Wth the ntroducton of tree structure, the proposed archtecture reduces the optcal loss between the gant router and users, mantanng low unavalablty of the rng topology. In addton, two dfferent routes that do not share any optcal swtch are set to every user. Therefore, all users can contnue to communcate wth the gant router when any one of 2x2 optcal swtches fals. In Fgure 10, two dfferent routes for user 2 are shown as dotted arrows. -marked ports are unused because t s unable to set two dfferent routes to user who connects wth these ports. Due to usng all ports of a 2x2 optcal swtch (except -marked ports), ths archtecture reduces S compared to the duplex tree topology. IV. DESIGN METHOD In ths secton, a desgn method of the proposed archtecture s shown. Subject to : (s 1 1) s 2 s 3 s M N (10) max U U ( = 0, 1, 2,..., N 1) (11) max L L ( = 0, 1, 2,..., N 1) (12) s m s the number of 2x2 optcal swtches of a mth-stage rng. M s the number of rng stages of the network. Constrant (10) means that the number of users that can connect wth optcal swtches of Mth-stage rngs s equal to or larger than N. U s the guaranteed unavalablty that the network provder set based on SLA (Servce Level Agreement). L s the loss budget between the gant router and users. Under these constrants, the followng objectve functon s set n ths method. Objectve : mn S ( = 0, 1, 2,..., N 1) (13) S = s 1 (1 + s 2 (1 + s 3 (1 + s M )... )) (14) B. Desgn example In the followng desgn example, t s assumed that the number of users N s 2 10, the unavalablty of a 2x2 optcal swtch u s 10 6 and the nserton loss of the optcal swtch l s 1(dB). The guaranteed unavalablty U s set to The loss budget L s set to 29(dB) n reference to that of IEEE802.3av 10GE-PON (10Ggabt Ethernet-PON) [7]. Networks whose number of rng stages s M (M = 1, 2, 3,..., log 2 N ) are created as shown n Fgure 11. For smplcty, the number of 2x2 optcal swtches of a mth-stage rng s set to 2 x (x s a postve nteger), wth the excepton that that of a 1st-stage rng s set to 2 x + 1. The dfference of the number of optcal swtches between mth-stage rngs s mnmzed. All networks are created to meet constrant (10) n ths example. Fgure 12, 13 and 14 show max U, max L and S of each created network. Fgure 12 shows that all created networks

5 2nd-stage rng 1st-stage rng 2nd-stage rng 2nd-stage rng Fg. 10. Proposed archtecture (N = 16, M = 2). (a) M=1 (S 1 =17) (b) M=2 (S 1 =5, S 2 =4) (c) M=3 (S 1 =3, S 2 =2, S 3 =4) Fg. 11. Networks havng M rng stages (N = 16). meet constrant (11). Fgure 13 shows that networks whose number of rng stages s 4 M 10 meet constrant (12). Therefore, the network of M = 4 s selected as the soluton because t has the smallest S among 4 M 10. C. Comparson of the number of swtches S Fgure 15 shows S of the duplex tree topology and that of the network created by usng the proposed desgn method. Assumed condtons except N are same as the above desgn example. Notce that the tree topology and the rng topology reduce S compared to the proposed desgn method, but they cannot create the network whch meets all constrants under these assumed condtons. The proposed desgn method can create the network whch meets all constrants when the number of users s 2 < N < The network created by usng the method reduces S compared to the duplex tree topology, except when N = 2. For example, t reduces S by 28% when N = V. CONCLUSION In ths paper, a novel optcal aggregaton network archtecture usng Mach-Zehnder type 2x2 optcal swtches s proposed. The proposed archtecture conssts of small-szed rngs that are connected lke a tree topology. The desgn method of the proposed network archtecture s also ntroduced n ths paper. The example shows that a hgh-avalablty and lowoptcal-loss optcal aggregaton network s desgned at 28% fewer optcal swtches compared to a duplex tree topology when N = 2 10, U = 10 6 and L = 29(dB).

6 N=2 10 N=2 10 Constrant( =10-6 ) Duplex tree( =2046) Fg. 12. max U of created networks. Fg. 14. S of created networks. N=2 10 Constrant( =-29) Fg. 15. S of duplex tree topology and that of created network. Fg. 13. max L of created networks. ACKNOWLEDGEMENT Ths work was supported by the Japan Socety for the Promoton of Scence s (JSPS) Grant-n-ad for Scentfc Research (C) REFERENCES [1] [2] M. Pckavet, et al, Worldwde Energy Needs for ICT: the RISE of Power-Aware Networkng, IEEE ANTS 2008, Bombay, Inda, December [3] D. McPherson, ATLAS Internet Observatory, ISOC Researchers, IETF76, Hroshma, Japan, November [4] H. Takeshta, et al, Hgh-energy Effcent Layer-3 Network Archtecture based on Soltary Unversal Cloud and Optcal Aggregaton Network, COIN 2010, TuC1-2, pp , Jeju, Korea, July [5] K. Nashmoto, PLZT Wavegude Devces for Hgh Speed Swtchng and Flterng, OFC/NFOEC 2008, OThE4, San Dego, USA, Aprl [6] ITU-T Recommendaton G.983.1, Broadband optcal access systems based on Passve Optcal Networks (PON), January [7] IEEE Standard 802.3av, Part 3: Carrer Sense Multple Access wth- Collson Detecton (CSMA/CD) Access Methodand Physcal Layer Specfcatons, October 2009.